5Treatment Closed reduction Revision options should target the underlying etiology.1- Tensioning or Augmentation of soft tissues2- Capsulorrhaphy3- Trochanteric advancement4- Correction of malpositioned of components5- Improving the head – neck ratio
6Surgical Approach75% to 90% of dislocations are in the posterior directionDislocation rate was 5.8% after a posterior approach versus 2.3% after an anterolateral approach(P < 0.01).Woo RY, Morrey BF: Dislocations after total hip arthroplasty. J Bone Joint SurgAm 1982;64:
7Surgical approchesA recent meta-analysis involving 13,203 procedures dislocation rate :3.23% Posterior approach2.18% Anterolateral, approach1.27% Transtrochanteric, approach0.55% Direct lateral approach.Masonis JL, Bourne RB: Surgical approach, abductor function, and total hi arthroplasty dislocation. Clin Orthop ;405:46-53.
8Surgical approach Larger heads (32 mm versus 22 and 28 mm) Definitive posterior soft-tissue repairThese two influential elements (head size and soft-tissue tension) therefore may reduce or eliminate the disadvantage of the posterior approach with respect to instability.Goldstein WM, Gleason TF, Kopplin M, Branson JJ: Prevalence of dislocation after total hip arthroplasty through a posterolateral approach with partial capsulotomy and capsulorrhaphy. J Bone Joint Surg Am 2001;86:2-7.
9Soft-Tissue Tension Meticulous reconstruction of the posterior capsule and short external rotators after a posterior approach was shown to reduce dislocation from 4.1% to 0.0% at 1-year followup in a study of 395 patients.Pellicci PM, Bostrom M, Poss R: Posterior approach to total hip replacement using enhanced posterior soft tissue repairClin Orthop 1998;355:
10Soft-Tissue TensionSoft-tissue tension also can be greatly affected by femoral offsetTrochanteric nonunion increased the dislocation rate sixfold (17.6% versus 2.8%; P < 0.001).large mismatch between femoral head size and acetabular component size(>64 mm cap <26 mm head )
11Component Positioning Cup abduction of 40° ± 10° is considered to be the “safe zone” of lower dislocation risk.Cup anteversion should be 20° ± 5°Outside this safe range, dislocation in one study increased fourfold (6.1% versus 1.5%; P < 0.05)Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR: Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am 1978;60:
12Component Positioning The pelvis of a patient in the decubitus position may be significantly adducted and anteverted relative to the table.Adequate acetabular anteversion may be more critical with a posterior approach because it reduces forces on weakened posterior soft tissues
13ImpingmentImpingement occurs when the prosthetic femoral neck impinges against the liner or other sessile object, such as cement, osteophyte, or heterotopic ossification .head-to-neck ratio is important. Components with higher ratios impinge less readily
15Head sizeThe improved head-to-neck ratio reduces component impingement and increases ROM.Larger heads are seated deeper within the acetabular liner, requiring greater translation before dislocation “jump distance”
16Head sizePolyethylene wear increases with larger heads and thinner liners, and wear leads to periprosthetic osteolysis and the potential for loosening.
18Surgeon ExperienceIn their study of more than 4,000 primary found that surgeons who had performed fewer than 30 procedures had a markedly higher dislocation rate (approximately twofold)Hedlundh U, Ahnfelt L, Hybbinette CH, Weckström J, Fredin H: Surgical experience related to dislocations after total hip arthroplasty. J Bone Joint Surg Br 1996;78:206-2